This invention relates to aqueous conductive polyaniline dispersions having enhanced viscosity. It also relates to electronic devices including layers made from such polyaniline dispersions.
Electrically conductive polymers have been found to be useful in electronic devices such as light-emitting diodes (LEDs), photodetectors and photovoltaic cells. It is well known to use a layer of conductive polymer, such as polyaniline (PANI), between the inorganic anode and the light-emitting or photosensitive layer. The conductive polymer layer is referred to variously as part of a bilayer anode, a hole-injection layer or a buffer layer. Such systems have been described in, for example, Yang, U.S. Pat. No. 5,723,873.
Useful synthetic procedures for the preparation of polyanilines are well known. For example, the aniline monomer can be treated with ammonium persulfate in excess hydrochloric acid in water. Other chemical procedures have been described in detail in Green, A. G., and Woodhead, A. E., xe2x80x9cAniline-black and Allied Compound, Part 1, xe2x80x9d J. Chem. Soc., 101, pp. 1117 (1912); and in U.S. Pat. Nos. 4,442,187, 4,321,114, and 5,160,457. The resulting polyaniline can have a variety of chemical forms. For the unsubstituted polyanilines, these are referred to as the leucoemeraldine, protoemeraldine, emeraldine, nigraniline, and tolu-protoemeraldine forms. In the presence of excess acid in water, the nitrogens of the polyaniline can be protonated to form a salt. Another useful synthetic method based on oxidative polymerization for preparation of polyanilines is enzymatic template polymerization disclosed in U.S. Pat. No. 6,018,018.
The thickness of the PANI layer needed depends to some extent on the surface roughness of the metallic conductive layer. Thicker layers are needed as the surface roughness increases. In order to prepare layers of increased thickness, it is desirable to have dispersions of PANI with high viscosity. Moreover, to reduce cost, it is desirable to have increased viscosity at low solids concentration.
The present invention is directed to a polyaniline/second polymer complex made by polymerizing anilines, each of the anilines having Formula I below, by oxidation in aqueous solution in the presence of a high molecular weight second polymer having a polymeric unit with at least one sulfonic acid group, having Formula II below. 
where in Formula I:
n is an integer from 0 to 4;
m is an integer from 1 to 5, with the proviso that n+m=5; and
R1 is independently selected so as to be the same or different at each occurrence and is selected from alkyl, alkenyl, alkoxy, cycloalkyl, cycloalkenyl, alkanoyl, alkythio, aryloxy, alkylthioalkyl, alkylaryl, arylalkyl, amino, alkylamino, dialkylamino, aryl, alkylsulfinyl, alkoxyalkyl, alkylsulfonyl, arylthio, arylsulfinyl, alkoxycarbonyl, arylsulfonyl, carboxylic acid, halogen, cyano, or alkyl substituted with one or more of sulfonic acid, carboxylic acid, halo, nitro, cyano or epoxy moieties; or any two R1 groups together may form an alkylene or alkenylene chain completing a 3, 4, 5, 6, or 7-membered aromatic or alicyclic ring, which ring may optionally include one or more divalent nitrogen, sulfur or oxygen atoms; and
in Formula II:
R2 is a polymeric unit selected from styrene, substituted styrene, vinyls, vinyl aromatics, acrylates, methacrylates, and combinations thereof;
a is an integer from about 1 to about 10; and
b is a number sufficient to give a molecular weight greater than 100,000.
The present invention is directed to a composition including a polyaniline complexed with a second polymer having a high molecular weight, the polyaniline comprising aniline monomer units, each of the aniline monomer units having a formula selected from Formula III below and Formula IV below, the second polymer having Formula II above: 
Where in Formula III and Formula IV:
n is an integer from 0 to 4;
m is an integer from 1 to 5, with the proviso that n+m=5; and
R1 is independently selected so as to be the same or different at each occurrence and is selected from alkyl, alkenyl, alkoxy, cycloalkyl, cycloalkenyl, alkanoyl, alkythio, aryloxy, alkylthioalkyl, alkylaryl, arylalkyl, amino, alkylamino, dialkylamino, aryl, alkylsulfinyl, alkoxyalkyl, alkylsulfonyl, arylthio, arylsulfinyl, alkoxycarbonyl, arylsulfonyl, carboxylic acid, halogen, cyano, or alkyl substituted with one or more of sulfonic acid, carboxylic acid, halo, nitro, cyano or epoxy moieties; or any two R1 groups together may form an alkylene or alkenylene chain completing a 3, 4, 5, 6, or 7-membered aromatic or alicyclic ring, which ring may optionally include one or more divalent nitrogen, sulfur or oxygen atoms.
The present invention is also directed to a method for the preparation of an aqueous dispersion of polyaniline, wherein aniline monomers are polymerized by oxidation in aqueous solution in the presence of a high molecular weight second polymer having a polymeric unit with at least one sulfonic acid group. The second polymer is selected from styrene and substituted styrene sulfonic acid polymers; sulfonated vinylaromatic polymers; vinyl sulfonic acid polymers; sulfonated acrylate polymers; sulfonated methacrylate polymers and their copolymers. It should be noted that the high molecular weight second polymer having a polymeric unit with at least one sulfonic acid group can be used as templates in enzymatic polymerization. In another embodiment, the present invention is directed to an organic electronic device having at least one layer including the polyaniline/second polymer complex described above.
As used herein, the term xe2x80x9cpolyanilinexe2x80x9d is intended to include polymers made from substituted and unsubstituted aniline monomers, unless the context is clear that only the specific non-substituted form is intended.